A normal heartbeat involves generation of an electrical impulse and propagation of the electrical impulse across the heart, which causes each chamber of the heart to appropriately contract. Sometimes aberrant conductive pathways develop in heart tissues, and disrupt the normal path of the electrical impulse. For example, anatomical obstacles or conduction blocks in heart tissue can disrupt the normal propagation of an impulse by causing the impulse to degenerate into several circular wavelets that circulate about the obstacles, thus disrupting normal activation within the heart tissue and chambers. Also, slow conduction zones in animal and human hearts constrained by anatomical or conduction blocks are believed to exist. Such a zone is a localized region of the heart tissue which propagates an impulse at a slower speed than normal heart tissue thus sometimes resulting in errant, circular propagation patterns or reentrant pathways. Reentrant pathways provide the substrates for the re-excitation of a region of cardiac tissue by an excitatory wavefront. Reentry may continue for one or more cycles and may sometimes result in tachycardia. Reentrant ventricular tachycardia (VT) is an abnormally rapid ventricular rhythm with aberrant ventricular excitation (wide QRS complexes), usually in excess of 150 per minute, which is generated within the ventricle of the heart as a result of a reentrant pathway.
To treat VT, it is desirable first to determine the physical location of the aberrant pathways. Once located, the heart tissue in the pathway can be ablated and destroyed by heat, chemicals, and/or other means. Heat can be generated in the targeted tissue using, for example, radio frequency (RF) energy, microwave energy, ultrasonic energy, or lasers to effect the ablation lesion. Ablation can remove the aberrant conductive pathway, restoring normal myocardial contraction. More specifically, to treat VT, the targeted conduction zone must be located and destroyed (or partially destroyed), with the goal of eliminating the conduction zone's ability to conduct electrical impulses.
In order to determine the physical location of the aberrant pathways, physicians have performed entrainment mapping. For example, entrainment mapping of re-entrant tachycardia is often used for identifying critical pathways of aberrant intracardiac conduction. Concealed entrainment of an arrhythmia requires that a post-pacing interval (PPI) be obtained. For example, in one protocol, concealed entrainment of an arrhythmia requires, among other criteria, that a PPI be within approximately 20 ms of a tachycardia cycle length. However, existing devices do not allow PPI measurements be obtained efficiently and conveniently. Particularly, when a pacing signal is routed to a biopotential sensing catheter that is connected to a diagnostic recording system, the biopotential recordings from the catheter can be obscured. This can be the result of the differential between the pacing signal (e.g., generally in the range of tens of volts) and an intracardiac biopotential (e.g., generally in the range of several millivolts). Recording amplifiers' responses to large transient spikes (e.g., step response of a signal processing chain) can also cause a variety of phenomenon, such as, saturation, overshooting, ringing, that can obscure biopotential recordings. As a result, a user may be required to manually manipulate existing software and manually process data in order to obtain a desired information associated with a particular biopotential recording.
Furthermore, existing software may automatically clip off valuable data associated with signal on a pacing channel, thereby making it difficult for a user to obtain desired information from a diagnostic recording. FIG. 1 illustrates an example of a display window 100 displaying data 102 that are generated using existing systems. Data 104 (shown in dotted-line) beyond the display window 100, including valuable biopotential data 106, are being clipped off by existing software because they are out of range. In such cases, in order to obtain a PPI, a user may need to modify existing software to search for the biopotential data 106. After the biopotential data 106 is located, the user may then need to manually measure or calculate a duration between a pace signal and the biopotential data 106 to obtain the PPI. This lengthens the amount of time necessary to diagnose a patient, and can complicate a diagnostic procedure.
Thus, there is currently a need for an improved device and method for obtaining biopotential data, and more specifically, for obtaining a post-pacing interval.